Hello Ripoathoa98
You cannot add the Swiss Travel Pass to your account.
For routes where the Swiss Travel Pass grants unlimited free travel, you simply show the PDF document with the QR code, together with your physical passport. No other ticket is needed.
When travelling on routes where the Swiss Travel Pass grants a discount of 50%, or if you want to upgrade your 2nd class Swiss Travel Pass to travel in 1st class, you can simply choose the “Half Fare Card” option, as the Swiss Travel Pass works as a Half Fare Card on that routes.
On routes where the Swiss Travel Pass grants 25% off, for example to Jungfraujoch mountain station, you cannot book tickets through sbb.ch. You have to purchase it from the railway operator’s site, for example, Jungfrau railways. SBB can either sell full fare or half fare tickets.
https://www.jungfrau.ch/en-gb/jungfraujoch-top-of-europe/buy-jungfraujoch-ticket/
I suggest using the SBB Mobile app to purchase additional tickets. How to activate the option there, I described to another user in this post (see link below). In your case with the Swiss Half Fare Card, instead of choosing “Half Fare Card”, simply choose “GA travel card” for the class for which your Swiss Travel Pass is valid. The GA travel card it is the resident equivalent of the tourist’s Swiss Travel Pass and has the same coverage as the Swiss Travel Pass. When entering a route, the app will then tell you whether the route is fully covered or not (or you look up the map of validity):
https://community.sbb.ch/d/26418-how-can-i-save-the-info-of-swiss-half-fare-card/2
Kind regards,
Roland